Biomedical subjects

J Grapperon

Publications and source records attributed to J Grapperon.

14 recordsLinked to original sources

PubMed2005

[Exploration of traumatic brain-injury attention difficulty by event-related potentials].

OBJECTIVE: To specify, in cognitive processing leading to an action, the localization of difficulties in attention following severe, traumatic brain injury. METHOD: Stimulus-locked and response-locked event-related potentials were recorded during a Stroop task in 25 patients with traumatic brain injury and 25 control subjects approximately 4 months after the accident. The latency and amplitude of the waves were compared between the two groups and correlated with clinical data. RESULTS: The reaction times of brain-injured patients were significantly longer than those of the control group, but neither the number of errors nor the interference differed between the groups. Electrophysiological recordings showed early abnormalities between 100 and 200 ms after stimulus onset. The key area could be the medial occipitotemporal side connected with frontal regions. Recordings also showed disruptions in motor program monitoring, which implied frontomedial areas. CONCLUSION: This protocol allows for precisely dating cognitive abnormalities. Future studies should relate cognitive with neuropsychological abnormalities and examine the possibilities of later regression.

Adult↗

PubMed2004

[Auditive and somato-sensory event-related potentials in comas: prognostic value for awakening, social and professional reinstatement].

OBJECTIVE: To appreciate prognostical value of event-related potentials in comatose states and the influence of the stimulation's modality. PATIENTS AND METHODS: Thirty-five patients were recorded with the auditory modality whose thirteen were also recorded with the somesthetic modality. They were free of sedation except for five. For 21 patients out of coma, it was possible to get information about their social readaptation 14 months later. RESULTS: When present, cognitive components predict awakening in 100 % of the cases, but only 50 % of the patients who awake had these components. The somesthetic modality seemed to enlarge their detection, but did not improve short-term forecasts. We could not confirm their absence could hamper social reinstatement. CONCLUSION: Event-related potentials are strengthened as having excellent positive prognostic value. Further studies should clarify the interest of the somesthetic modality, and the possibility to get remote prognostic.

Adolescent↗

PubMed2004

Response selection and motor areas: a behavioural and electrophysiological study.

OBJECTIVE: The involvement of the supplementary motor areas (SMAs) and primary motor areas (M1s) in motor processes was studied. METHODS: A between-hand choice and a simple reaction time (RT) task were mixed in a precueing paradigm. Laplacians were estimated by the source derivation method from the electroencephalogram recorded over the SMAs and M1s. RESULTS: RT was shorter in the simple than in the choice RT task. Response-locked averages showed a negative potential over M1 contralateral to the response and a positive wave over M1 ipsilateral. This ipsilateral positivity was much smaller in the simple than in the choice RT task, whereas the contralateral negativity was not different. A negativity preceding the activations of the M1s developed over the SMAs. This negativity was larger in the choice than in the simple RT task. CONCLUSIONS: In light of previous results, the present data confirm that, in between-hand choice tasks, response execution is implemented by an activation of the contralateral M1 and by an inhibition of the ipsilateral M1. SMAs and contralateral M1 appear hierarchically organized, the SMAs being more involved in response preparation and M1s in response execution. The task-dependent inhibition of ipsilateral M1 could reflect an active suppression of the erroneous response in the choice task. SIGNIFICANCE: The task context in which one movement is executed can affect the pattern of activities recorded over cortical motor structures. Cognitive context is of importance for understanding the nature of the motor command.

Adult↗

PubMed2004

Response monitoring without sensory feedback.

OBJECTIVE: The elicitation of an evoked potential, the 'error negativity' (Ne) when subjects commit errors in speeded tasks, is often taken as an index of response monitoring processes. The presence of a Ne-like wave on purely correct trials challenges the current conceptions about the nature of such a monitoring system. Here, we evaluate the possibility that the Ne-like wave on correct trials is merely due to reafferences, and at the same time, we test directly the general opinion according to which the Ne is generated by an internal signal. METHODS: We studied the presence of a Ne-like wave in a completely deafferented patient. The patient performed two reaction time (RT) tasks: a two-responses RT task and a go/no-go task. RESULTS: In this patient, a Ne occurs on errors, on incorrect EMG activations, and on purely correct responses. On errors, the Ne was clearly followed by an error positivity (Pe). CONCLUSIONS: The Ne and the Ne-like wave are not generated by reafferences. This similarity is a further argument to consider that these two waves are of same nature. SIGNIFICANCE: The present data demonstrate that sensory information is not mandatory for the brain to monitor and correct ongoing responses.

Afferent Pathways↗

PubMed2004

[Effect of an early visual encoding defect on attentional function: a study of daltonism using the Stroop test].

The Stroop color-word test is often used to assess attentional function. In this study we investigated whether dyschromatopsia affects the results of this test, and in that case which are the attentional consequences of this color-vision trouble. Event-related potentials were recorded on 19 dyschromatopsic subjects when submitted to a video-displayed Stroop test, and compared to those of 19 control subjects. Results showed that reaction times of dyschromatopsic subjects, although generally longer than those of controls, had normal interference and facilitation effects. Potentials evoked by neutral stimulations were delayed for P2 and P3 waves, and those evoked by word-containing stimulations showed delays for N2b (N320) and P3 waves. The premotor potential appeared modified in dyschromatopsic patients, whereas error negativities, or correct response negativities were identical to those of control subjects. We conclude that dyschromatopsia affects negatively the performance in the Stroop test, at sensory levels which are reflected by evoked potentials, but without important consequences on attentional function. In particular, dyschromatopsia did not alter significantly the attentional focusing on the chromatic aspects of the stimulus.

Adult↗

PubMed2003

Error negativity on correct trials: a reexamination of available data.

The error negativity, an EEG wave observed when subjects commit an error in a choice reaction time (RT) task, is often considered as a sign of error detection. Recently, reports of Ne-like waves on correct responses did challenge this interpretation. It has been proposed, however, that these Ne-like waves result either from an artifactual contamination of response-locked activities by stimulus-locked ones, or from an implicit monitoring of the time elapsing during the RT. Our aim was to reprocess published data: (1) to compare the shape and amplitude of EMG-locked and stimulus-locked ERPs on correct trials, and (2) to compare the size of the EMG-locked Ne-like waves obtained on fast and slow trials. The results neither support the artifact hypothesis nor the RT monitoring one. Therefore, it seems that the Ne-like waves observed on correct trials do correspond to a Ne, which suggests that the Ne has a broader significance than just error detection.

Adult↗

PubMed2000

Is the 'error negativity' specific to errors?

When subjects make an erroneous response in a choice reaction time task, an error negativity, or error-related negativity (N(E)/ERN), peaking at about 100 ms after EMG onset, has been described. This wave is often considered to be absent on correct response trials. We report a small N(E)/ERN wave on correct response trials during a choice reaction time task in which surface Laplacians were estimated by the source derivation method. This wave is well focused at FCz, and its time course is the same for correct responses trials, incorrect sub-threshold EMG activation trials, and error trials. Current source density maps, also indicate a focus at FCz. A second experiment showed the existence of a N(E) at FCz on correct trials during a simple RT task. Rather than an error detection process per se, we propose that the N(E)/ERN reflects either a comparison process leading secondarily to error detection, or an emotional reaction.

Adult↗

PubMed1999

[Cervical spine and accelerations in aeronautical environment: ergonomic and electromyographic approaches].

Both, an analysis of the variation of the electromyographic signal with respect to the acceleration endured by flying personnel and an ergonomic evaluation of pilot activity, have been achieved. The authors show then the inadequacy of the muscular response to the high Gz with rapid on set and its functional incompatibility to provide simultaneously a correct bearning contraction and a good mobility of neck. Consequently, the authors propose an instruction of flying personnel about these risks and they determine a specific muscular training.

Acceleration↗

PubMed1998

[The contribution of cognitive evoked potentials to knowledge of mechanisms on the Stroop test].

The Stroop test is based on interference between reading and naming of incongruent color words. To decide whether this conflict was of perceptual or motor origin, event-related potentials were simultaneously recorded. Since the components of these potentials are dependent on the progression of information processing, their changes related with the nature of the stimulation should provide information about the mechanisms underlying the conflict. Evoked potentials were recorded from three midline leads in 18 healthy subjects during reading and naming tasks. The 216 stimulations were the words "red, green and blue" presented in either a congruent or incongruent color, or in a neutral color. The behavioral Stroop effect did not affect the P300 latency, suggesting that the conflict occurs in the motor system. This was supported by the presence of a premotor negativity for incongruent stimulations, occurring between 400 and 205 ms before button press, and present in the naming condition only. Moreover, for the two conditions, congruent stimulations evoked positive potentials between 260 and 310 ms at the level of the occipital lead for reading and at the level of the frontal lead for naming. The possibility of an interaction of specialized channels for stimulation analysis at an early level is raised.

Adolescent↗

PubMed1994

[Can neurophysiologic tests differentiate between depression and dementia?].

In order to evaluate the clinical utility of neuro-physiological tests in distinguishing between depression and dementia, we compared quantified EEG and event-related potentials (ERP) in 13 depressed and 12 demented patients. Their cognitive functions were clinically assessed by the ERFC test. When scored with a discriminant function, EEG misclassified one patient and all were well classified with ERP. Nevertheless this exam could be clearly obtained in only 7 demented and 5 depressed patients. Although a therapeutic effect could not be absolutely discarded, these results show that these tests, when practicable, can be helpful when clinical diagnosis is uncertain.

Adult↗

PubMed1993

[Central and peripheral nervous system motor conduction rate in HIV infection].

In order to assess the central motor pathways of HIV-infected patients motor evoked potentials were recorded on the upper limbs after transcranial and cervical magnetic stimulations and compared with peripheral conduction velocities. Motor evoked potentials were measured on both sides of 28 patients, mostly at the AIDS stage. Our results showed that although peripheral neuropathy was often found, central motor pathways did not appear, at the level they were tested, to be directly or indirectly damaged by the virus. On the contrary, some hyperexcitability seemed to be present.

Acquired Immunodeficiency Syndrome↗

PubMed1988

Effects of high pressure on nervous conduction velocity in man.

The velocities of motor and sensory nervous conduction and of neuro-muscular transmission were measured in four subjects during a simulated dive at 4.6 MPa (46 bars). The results show an increase in motor distal latency in the ulnar nerve, especially during decompression, with reversibility of the effect on return to ambient conditions. The hypothesis of an interaction of dissolved gases with the membranes of ischaemic cells is proposed.

Adult↗

PubMed1986

[Changes in nerve conduction velocity as a result of hyperbaria in man].

Nervous conduction was measured in 27 subjects before and after compression in ternary mixture (helium, nitrogen and oxygen) ranging from 5,5 to 12 ATA. Among the eleven parameters studied, three showed an acceleration of the nervous conduction in the distal part of the sensitive and motor fibers. Although no precise mechanism can be established, different factors, in particular the role of ischemia, are discussed.

Adult↗

PubMedDate not supplied

[Stroop test and schizophrenia].

Utilization of the Stroop test with schizophrenic subjects is reviewed from 32 studies published since 1960. This test, in which subject has to name the color of color-words which are congruent or incongruent, is much used as a selective attention test. Its specific disturbance in schizophrenics would confirm the overload of consciousness with unsignificant non filtered information, probably due to lowering of frontal functions. Stroop effect is not always raised in these patients, especially when general slowing is taken into account. Technical differences modify the test power and can explain contradictory results. The thought disorder symptom seems the most correlated with the results of the test, and particular sensitiveness of paranoïd form has been argued. Neuroleptics do not seem to act on Stroop effect. Factors explaining the great variability of patients in this test are not fully put in light. One hypothesis, already raised, is that the test is linked to a particular attentional constitutional aptitude, and whose relations with the illness are to be explained.

Antipsychotic Agents↗